The difference between solder mask and paste mask

In the PCB design, basically design engineer need to make two layers with solder mask layer and paste mask layer, the following is a brief description about the difference between these two types of layers.

Solder mask layer: the patterns on solder mask layer won’t be covered by solder mask ink, but the remaining area will be covered by solder mask ink, generally the solder mask pads are slightly larger than the copper pad by 0.102mm.

Paste mask layer: the soldering layer, also called the steel mesh layer, needs to be set for the surface mount components, generally the same as the copper pad size.

Normally solder mask layer is used for PCB manufacturing in PCB factory, and there are different colors for solder mask, like green, blue, black, white, red etc. Solder mask is one of the most important manufacturing process in PCB fabrication.

Paste mask layer is only used for fabricating solder stencils which used in the process of PCB assembly, paste mask layer has nothing to do with the manufacturing of print circuit boards.

Sometimes, if the gerber file doesn’t include paste mask layer, stencil engineers can make paste mask layer according to the solder mask layers, but basically it needs to be confirmed by customers if the opening pads on paste mask layer is all necessary for the fabrication of solder stencils.